PURIFICATION AND CHARACTERIZATION OF DNA-LIGASE-III FROM BOVINE TESTES - HOMOLOGY WITH DNA-LIGASE-II AND VACCINIA DNA-LIGASE

Mammalian cell nuclei contain three biochemically distinct DNA ligases . In the present study we have found high levels of DNA ligase I and D NA ligase III activity in bovine testes and have purified DNA ligase I II to near homogeneity. The high level of DNA ligase III suggests a ro le for this enzyme in meiotic recombination. In assays measuring the f idelity of DNA joining, we detected no significant differences between DNA ligases II and III, whereas DNA ligase I was clearly a more faith ful enzyme and was particularly sensitive to 3' mismatches. Amino acid sequences of peptides derived from DNA ligase III demonstrated that t his enzyme, like DNA ligase II, is highly homologous with vaccinia DNA ligase. The absence of unambiguous differences between homologous pep tides from DNA ligases II and III (10 pairs of peptides, 136 identical amino acids) indicates that these enzymes are either derived from a c ommon precursor polypeptide or are encoded from the same gene by alter native splicing. Based on similarities in amino acid sequence and bioc hemical properties, we suggest that DNA ligases II and III. Drosophila DNA ligase II, and the DNA ligases encoded by the pox viruses constit ute a distinct family of DNA ligases that perform specific roles in DN A repair and genetic recombination.